Enterprises go to great lengths to ensure that their data is properly backed up and always available online. Information has become the lifeblood of organizations and any access downtime whatsoever is problematic.
In addition, many times an organization wants to maintain versions of its information so that desired states of the information can be acquired as needed. States of data or information is generally handled via snapshot technology.
To avoid delays associated with accessing primary data when that primary data is being backed up, enterprises will back up snapshots of the primary data, which are being maintained as read-only copies of the primary data. So, access to the primary data is always available even when the primary data is being actively backed up because the backup occurs off a snapshot.
A snapshot of a disk volume takes the original volume (origin or source) and a second volume as inputs and creates a new snapshot volume, which is a virtual volume that uses both of these volumes underneath for its operations. This second volume is often referred to as a “Copy On Write” (COW) device. When there are multiple snapshots for the same origin volume then the complexity to manage the COW devices grows and many problems are encountered.
Some issues associated with managing and creating COW devices include: fragmentation, predicting size of COW devices in advance, optimal use of disk space, etc.